Propane dewaxing



April 6, 1937. H Q FORREST 2,076,141

PROPANE DEWAXING Filed March 8, 1935 Propcuw APP/"0,02% 5$LLL Patented Apr. 6, 1937 1 UNITED STATES PATENT OFFICE momma: mswaxme Henry 0. Forrest, Teaneck, N. J., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Application March 8, 1935, Serial No. 10,060

4 Claims. (Cl. 62-170) 5 method of utilizing the refrigeration value of cold products and a method of continuously and countercurrently cooling an oil-wax slurry.

The object of my invention is to avoid the neces'sity of scraped surface chillers and at the same time to utilize the refrigeration value of cold filtrate for cooling further amounts of diluted oil-wax mixture.

A further object is to provide a method and means for continuously chilling a propane-oil mixture by self-refrigeration in a plurality of stages without shock chilling in any stage. Other objects will be apparent as the detailed description of my invention proceeds.

In practicing my invention I employ a rela- '20 tively large number of chilling stages so that there will be no appreciable pressure drop between any stage and the next succeeding stage, the wax slurry being introduced at the bottom of each stage and from the top of said stage to the 5 bottom of the next stage so that the summation of the heads of liquid in the various stages and the pressure drop due to the flow through the pipes connecting the various stages are substantially enough to account for the total pressure drop throughout the cooling system. In

order to, utilize the refrigerative value of the. cold filtrate, I pass said filtrate through coils in the vapor space of each chilling stage consecutively from the coldest to the warmest thereof, so that in each stage there will be about the same temperature differential between the propane-oil mixture and the cooling coils in the vapor space. The cooling in each stage is effected by the vaporization of propane from the mixture, the propane vapors being condensed on the coils in the vapor space sothat the condensate falls back into the liquid like rain, thus not only cooling the liquid but maintaining a constant diluent ratio.

The invention will be more clearly understood from the following description read in connection with the accompanying drawing, which forms a part of this specification and in which I have shown a diagrammatic plan of my improved system with parts thereof shown in vertical section.

The oil to be dewaxed may be a distillate or residual stock from any type of a crude petroleum or it may be any other wax-bearing oil which may be subject to the propane dewaxing process. In my preferred example I will describe the dewaxing of an S. A. E. 50 Mid-Continent distillate lubricating oil stock. I will describe the use of propane as a preferred example of my refrigerant, but it should be understood that other normally gaseous refrigerants may be used.

The-waxy oil stock from storage tank to is forced by pump ll through line l2 to oil-propane mixer l3 where it is admixed with propane from line H and storage tank l5. If the oil is not at a sufiiciently high temperature to bring about the complete solution of the waxy oil in the propane, a heating means may be supplied in the mixer or heat exchange devices may be employed in lines l2 or M. The warm solution of waxy oil in propane, preferably employing about two volumes of propane per volume of oil, is introduced by pipe H5 at the base of the first cooling stage ll.

Each of the cooling stages is carried out in a pressure vessel I8 which is surrounded by suitable insulating material. An overflow pipe 20 conveys liquid from an intermediate point of the pressure vessel to the bottom of the next vessel. The flow of liquid through line 20 is regulated by valve 2| which is in turn controlled by a float device 22 which is illustrated as being mechanically connected to .the valve, but which in actual practice would be connected to the valve through a magnetic clutch so that there would not have to be a packed joint.

- The second stage of the cooling process is effected in pressure vessel 23 which is identical in structure with vessel l'l. The last steps of the cooling process are efliected in chambers 24 and 25. The total number of chilling stages will depend somewhat upon the nature of the oil to be chilled, the desired pour points of the finished oil, etc. and will also depend on whether or not wax crystallization regulators such as described in Davis Patent No. 4,815,022, MacLaren Patent No. 1,963,917, etc. are used. I In general, I may employ from six to twelve of such stages and in the present example I prefer to employ ten stages and to effect a pressure drop of about ten to twelve pounds per stage. The oil-wax slurry leaving the final stage 25 is conducted through line 26 to the base of chiller 21. Propane from storage tank I5 is conducted through line 28 and line 29 to cold propane storage tank 30 wherein it is fiash chilled, and it is then introduced through line 3| and valve '32 into the upper part of chiller 21, the amount of cold propane being controlled by any suitable mechanism or valve *82. Propane is removed from chiller 21 through line 34 in amounts equivalent to the amounts introduced so that the ratio of propane to oil-wax mixture may be held constant. The cold propane is preferably introduced on bubble plate 35 and it passes therefrom through downcomer 36 to bubble plate 31 before coming in direct contact with the cooled wax slurry. Pro

pane vapors bubbling up under caps 38 are partially condensed in the cold propane and by their condensation they give up enough heat to bring this cold propane into equilibrium with the temperature of the cold wax slurry, thereby avoiding shock chilling when the cold propane passes through downcomer 39 into the body of the chilled oil-wax'mixture.

The chilled slurry fromchiller 21 is passed through line 40 to a storage tank 4| which is connected by line 42 to the holding compressor gas line 43. Slurry from tank 4| is forced by pump 44 or by fluid pressure into continuous filter 45, the wax cake being withdrawn through line 46 by pump or screw conveyor 41 through line48 into wax melter 49 which is heated by closed steam coil 50. The wax is withdrawn through line 5| and the propane is withdrawn at a pressure of about 200 pounds through line 52 directly to condenser 53.

The cold filtrate from filter 45 is passed by line 54 to filtrate collector 55 which is vented through line 66 to holding compressor gas line 43. This cold filtrate is forced by pump 5'! under'a pressure of about 200 pounds through line 58, coil 59, line 60, coil 6|, line 62,,coi1 63, line 64, coil 65 and line 66 to high pressure propane still 81.

' Still 61 is provided with closed steam heating coil 63 which distills oil the propane through line 69 which leads to condenser 10. The oil is passed from the base of still 61 through pipe II and reducing valve 12 and it is then introduced into low pressure propane still 13 which is provided with steam coil 14. Finished oil is withdrawn from the base of the low pressure still through line l5. Propane from this still is withdrawn through line 16 to holding compressor gas line 43. Propane from cold storage tank 30 is introduced through line 11 to holding compressor gas line 43. Chiller 21 is connected through line 34 and line 18 to holding compressor gas line 43 and holding compressor 19'. Ordinarily valve 19 and valves are closed, but provision is made so that propane may be withdrawn from any of the chilling stages and introduced through line 8| to holding compressor gas line 43. Suitable means (not shown) are also provided for draining liquids out of the various chilling stages, washing the filter with hot naphtha, etc. Such expedients and other expedients are well known to engineers skilled in the art and will therefore not be described.

The mixture of waxy oil and propane which was introduced through line l6 into stage 11 may be at a temperature of about 130 F. and there may be about a 35 to 40 Rtemperature differential, so that the filtrate in coil 65 will be at a temperature of about to F. The oil leaving the first stage through pipe 20 may be at about 120 F. and it is cooled in stage 23 to F. by cold filtrate in coil 63 at about 80 F. With ten or twelve stages, I can thus reduce the temperature of the propane-oil-wax mixture to about 40 F., or even lower, at which temperature it may be introduced into one or a plurality of evaporative chillers to which propane is added (illustrated in the drawing as chiller 21). If it is desired to maintain a constant temperature differential in the various stages I may supplement the filtrate with cold propane or other chiliing medium. Likewise, I may supplement the countercurrent chilling action of the cold filtrate by removing some propane vapors through one or more of valves 80 and I may introduce cold propane into one or all of these stages in the manner described in connection with chiller 21.

It should be understood that the depth of liquid in each chiller should balance the pressure from the preceding chiller (no pressure drop between steps) so that the eil'ect is the same as if each stage were superimposed upon the preceding stage to give one high column. If a single column were used the liberated'propane would cause too much turbulence,-this is avoided by employing a long series of short columns as hereinabove described.

While I have described in detail a preferred embodiment of my invention, it should be understood that I do not limit myself to'the above details except as defined by the following claims, which should be construed as broadly as the prior art will permit.

I claim:

1. In apparatus of the class described, a plurality of closed chill chambers, means for introducing a liquid from an intermediate part of each -chill chamber to the base of the next following chill chamber, means actuated by liquid level control for regulating the amount of liquid flowing from each chamber to the following chamber, and means at the top of each chamber for reducing the pressure in said chamber and caus ing the vaporization of propane on the surface -of the liquid therein.

2. The apparatus of claim 1 wherein each of the chambers is provided with a cooling coil in the upper part thereof and wherein said cooling coils are connected in a series corresponding to the flow of liquids from each chamber to the next.

3. In a process for separating wax from oil by means of a normally gaseous diluent such as propane, the method which comprises continuously introducing a propane solution ofan oil-wax mixture into a chilling stage, chilling said mixture in said stage by vaporizing propane there;

from, continuously transferring the chilled liquid from said stage to a second stage, chilling the liquid in the second stage by vaporization of propane therefrom, and continuously transferring and chilling said solution in a plurality of further stages, the pressure at the bottom of each stage beingsubstantially equal to the pressure at the top of the prior stage, accelerating the vaporization of propane in each stage by passing a refrigerating fluid through the vapor space therein, and finally separating wax from diluted oil.

4. The method of claim 3 wherein the refrigerating fluid is the cold propane oil solution separated from the wax and wherein the cold solution is passed countercurrent to the passage of the oil propane solution through the chilling stages.

HENRY O. FORREST. 

